Steam cooling of gas turbine buckets is susceptible to debris generated downstream of filters, in that the debris may collect in radially outer extremities (tip turns) of the buckets that are to be cooled, thereby building up a cooling path blockage over time and reducing the cooling capability at the bucket tip by forming a layer of debris that insulates the hot bucket tip surfaces from the cooling medium.
This invention provides a cooling circuit arrangement which collects and traps debris present in the steam cooling medium in a region of the bucket cooling circuit where it does not effect the cooling task of the steam, i.e., upstream of the buckets.
More specifically, the path of the cooling steam supplied to the first and second stage buckets of a gas turbine manufactured by the assignee of this invention passes through a relatively low velocity steam manifold before exiting the manifold through higher velocity feed tubes which carry the steam to the buckets. At this location in the cooling path, centrifugal loads on the debris force the debris to collect in a radially outermost region of the manifold, away from the primary flow stream lines. To this end, the manifold extends radially beyond the bucket feed tubes to thereby create a recessed trap region which collects the solid particles and other debris under the centrifugal loading created by the rotating rotor. In the exemplary embodiment, here are ten such manifolds arranged in an annular array about the turbine rotor, each manifold segment extending approximately 36xc2x0.
Accordingly, the present invention relates to a gas turbine having a rotor and a plurality of stages, each stage comprising a row of buckets supported on a wheel mounted on the rotor for rotation therewith; and wherein the buckets of at least one of the stages are cooled by air or steam, the improvement comprising at least one axially extending coolant supply conduit communicating with a coolant supply manifold; one or more axially extending coolant feed tubes connected to the manifold at a location radially outwardly of the coolant supply conduit, the one or more feed tubes arranged to supply coolant to one or more buckets of at least one of the plurality of stages; the manifold extending radially beyond the one or more axially extending feed tubes to thereby create a debris trap region for collecting debris under centrifugal loading caused by rotation of the rotor.